In 2010, Volvo teamed up with Imperial College London (ICL) to begin work on a novel approach to stripping weight out of vehicles: replacing batteries with super capacitors. But these weren’t just any super capacitors—the electrical storage devices were integrated into the bodywork. Specifically, the research Volvo tapped into was an ICL professor’s investigation into structural carbon-fiber panels that double as super capacitors.

Three years on, Volvo’s research has brought forth some fruit, in the form of a capacitive trunk and an underhood panel capable of storing and releasing electrical energy. Volvo claims that further down the road, this technology could lead to a 15-percent reduction in weight for hybrid and electric vehicles by obfuscating the need for heavy chemical batteries. Capacitors can recharge and dump their energy far quicker than conventional batteries—ideal for short bursts of power and capturing braking energy. In a capacitor, two conductive surfaces are separated by a non-conductive dielectric; integrating the three elements into a circuit builds a charge, and within this field electrical energy is stored. Super capacitors earn their “super” stripes by packing surfaces with a greater overall area than regular capacitors and positioning them closer together.

Thinness and surface area are two things body panels and other structural automotive elements have in abundance. Volvo’s structural capacitive material consists of an outer and inner layer of conductive carbon fiber separated by a layer of fiberglass (the dielectric). Volvo doesn’t elaborate much on the conductive aspect of its carbon-fiber panels, but based on the lead researcher’s published works, it appears as though a carbon aerogel is embedded in the carbon-fiber weave. If you think this whole idea is slipping down the proverbial carbon nanotube, you’re close—aerogel is an advanced ultra-lightweight solid nanomaterial that’s ultra-porous and highly conductive, depending on its density. So while the carbon-fiber sandwich carries mechanical load, the aerogel carries the electrical load; as a bonus, the aerogel’s porosity increases each layer’s surface area by a claimed 100 times, making for a more powerful super capacitor.

So the technology is fascinating, and Volvo claims that just the underhood panel alone (essentially the plastic tray from which the wipers sprout) on its S80 test car is 50-percent lighter than the car’s conventional battery and capable of powering the engine’s stop-start system. Such weight savings and functionality is an accomplishment to be sure, but neither Volvo nor ICL have alluded to what would happen if, say, one of the conductive panels breaks. (These are crash-susceptible body panels, after all.) Lithium-ion batteries offer the threat of fire if ruptured—see Tesla’s latest woes for a backgrounder on that potential issue—but shorting a high-energy capacitor could bring its own set of problems. And let’s not get started on cost. Carbon fiber still isn’t cheap, and embedding it with nanotech like carbon aerogel—or whatever nanotech Volvo’s using to imbue the carbon fiber with more conductivity—is likely prohibitively expensive. Fender-benders might never be the same.

For now, however, the research is promising. As Volvo points out, stripping major weight out of a heavy component like a battery can have a spiral effect: Big weight reductions mean lighter support bits can be used. The lighter the rest of the components, the lower the energy needs of the vehicle, and thus the fewer super capacitors are needed, and the spiral continues. Mazda currently uses a super capacitor in its i-ELOOP brake-energy-recuperation system, and we could see this material working as an excellent energy-storage system for hybrids in the near future, but its replacement of an all-electric car’s batteries likely is many, many years away from large-scale viability.